As plastic materials for automotive connectors, there have been used, for example aliphatic polyamides (PA 66, PA 6) and polybutylene terephthalate (PBT).
However, aliphatic polyamides tend to absorb water to decrease modulus of elasticity, so that there have been a problem that when a connector made of an aliphatic polyamide is used in water or under conditions of high humidity, the connector may loose its firm fitting and even may be taken out. On the other hand, connectors made of PBT are heavy due to its high specific gravity. There is also a problem that heat resistance of PBT is not always sufficient.
Water absorption characteristics of aliphatic polyamides can be improved by combining it with an aromatic polyamide (see Japanese Patent Application No. 2-85,208).
However, such combination of aliphatic and aromatic polyamides may lead to poor moldability. Such poor moldability can be improved by elevating a molding temperature, but this gives rise to a new problem that where a connector of a certain shape is to be molded, it may sometimes stick in the mold.
In order to solve such problem of poor mold release associated with the use of an aromatic polyamide, an attempt to improve the mold releasability by the addition of a mold release agent to the aromatic polyamide has been proposed, for example, in JP-A-3-163,165. The mold release agent used therein includes metallic salts of higher fatty acids, for example calcium stearate and derivatives of aliphatic carboxylic acids such as aliphatic alcohol esters of montanic acid, which can also usable as form release agents for aliphatic polyamides.
It has been found, however, that when a mold release agent, for example disclosed in the above-mentioned JP-A, is added to a composition comprising an aromatic polyamide, the mold release agent may evolve gas and foam during a molding step to lead deterioration of properties of connectors obtained. This is because an aromatic polyamide has a higher melting point than an aliphatic polyamide so that a composition comprising an aromatic polyamide must be molded at a temperature higher than that of a composition comprising an aliphatic polyamide. That is, even if it is intended to prepare connectors from the aromatic polyamide composition containing the compound used as the mold release agent for aliphatic polyamide as mentioned above, such compound may decompose at the molding temperature to foam and cannot effectively function as the mold release agent, resulting in poor mold releasing of the connectors. Further, because of such poor moldability, there may be obtained connectors which sometimes do not have intendedly improved characteristics such as toughness.
An object of the present invention is to provide lightweight connectors which do not deteriorate their characteristics, such as toughness, by heating, and can be prepared with excellent molding workability.